1. Field of the Invention
The present invention relates to an electrical actuator which is used for controlling a throttle valve, an exhaust gas recirculation valve (EGR valve), supercharging pressure of a supercharger, and the like, which are used, e.g., in a motor vehicle.
2. Description of the Prior Art
Recently, a direct current (DC) motor is used as a driving source for an onboard (in-vehicle) electrical actuator for a motor vehicle. Since the environment in which the DC motor is used is high in temperature and, in view of the heat generation by electric current to flow through coils of the motor, it is obliged to use constituent elements made of a very high heat-resistance material.
However, the DC motors to be used as the driving source for the electrical actuator for various purposes are desirable to be manufactured at a smaller cost in as much a uniform specification as possible. For that purpose, the DC motors are often made of resins, and resins are used in parts requiring strength such as exterior parts and functional parts, e.g., an electrically insulating material for coil materials forming coils, or the like. In order to secure strength or accuracy of each constituent part made of a resin while in service at a high temperature, or from the viewpoint in that the electronic parts for driving the DC motor are sometimes contained inside the motor, due consideration must be taken in most cases to keep the ambient temperature of the DC motor to the lowest extent possible.
Especially, in case the electrical actuator is used for control of supercharging pressure of a supercharger, the electrical actuator is in most cases disposed near an exhaust gas passage or near a turbine of the supercharger which reaches a high temperature due to the heat of the exhaust gas of an engine of a motor vehicle. In such a case, the electrical actuator is used while being exposed to a high temperature as a result of receiving the radiant heat and, therefore, a higher heat resistance of the electric actuator is required as compared to actuators for the other purposes.
Since the conventional electrical actuator is constituted as described above, in case it is used under conditions of a high-temperature atmosphere, there is the following drawback, namely, due to the radiant heat from the heat generating member such as the exhaust gas passage of the engine, the turbine of the supercharger, or the like, the electrical actuator itself is heated to a high temperature, whereby the electromagnetic parts or the electronic parts inside the electrical actuator get out of order. In addition, in order for the electrical actuator to be fixed to the member for supporting it, a constituent part is required. However, the part for supporting the DC motor which serves as the driving source of the electrical actuator has a shape which is uniformly set. Therefore, there is a drawback in that another mounting part other than the DC motor itself must be prepared in order to change the part for mounting the DC motor to the mounted side depending on the purpose and the shape of the mounted side.